1. Field of the Invention
The invention relates to an optical waveguide for an optical cable with at least one optical waveguide which has a protective covering and a substantially rectangular internal opening which forms a chamber for accepting the optical fibers, in each case a number of ribbon conductors each having a plurality of optical fibers being accommodated in the chamber in the form of a ribbon conductor stack, and the optical waveguides having a bending plane with the smallest bending resistance and the ribbon conductors being arranged with their broad sides substantially parallel to this bending plane.
2. Description of the Related Art
GB-A 30,157,516 discloses an optical cable in which a circular opening which serves to accept a subunit provided with tension elements is provided inside a cable sheath. This subunit has a substantially approximately rectangular cross section and represents a flat, ribbon-shaped configuration. Provided in the interior is an opening in which two optical fiber ribbons are arranged between which only a very small spacing exists. In order to produce an excess length, the subunit is guided as a whole through an undulation device, so that after this production process the subunit has assumed an undulating structure. A space which corresponds to at least the excursion of the undulation is required in order to accommodate such an undulating structure. In addition, the undulation requires its own undulation process to be carried out, it being impossible for this undulation process to be carried out without a certain mechanical loading of the optical fiber ribbons.
DE-U 89 01 404 discloses an optical cable in which a ribbon conductor stack is accommodated in a tubular protective covering. This protective covering has a circular cross section. In order to guarantee the cohesion of the optical fiber ribbons inside the stack, firmly adhering connecting elements which fix the ribbon conductor stack are provided at specific spacings. However, such additional connecting elements represent not only an additional outlay, but they also cause a lower displaceability of the optical fiber ribbons inside the stack. Moreover, the connecting elements always also entail a mechanical loading of the ribbons.
An optical waveguide of this type is disclosed in German Offenlegungsschrift 30 27 743, the excess length of the optical fiber with respect to the protective covering of the optical waveguide being achieved when the optical fiber or fibers are inserted by being fed. In this way, the optical fibers acquire an approximately undulating shape, an additionally inserted gel-like filler stabilizing the optical fibers in this undulating structure.
However, in many instances it is desirable not to arrange individual optical fibers inside a protective covering, but to guide these in the form of ribbon conductors, which in particular substantially simplifies splicing technology. It is known from DE-A 24 59 997 to arrange a plurality of optical fibers adjacent to one another and to fix the latter at discrete points on a carrier sheet, for example of plastic material. The carrier sheet itself therefore does not extend in a straight line. Since the optical fibers extend freely outside these fastenings, it is possible to realize an undulating structure for them in these regions. However, it is to be borne in mind in this regard that fixing optical fibers at specific points is always accompanied by a certain mechanical loading in this region. The procedure in constructing a cable is such that a plurality of tensile elements, for example in the form of steel wires, are provided in a flat cable sheath, one or more ribbon conductors being arranged inside rectangular openings. The rectangular openings themselves are chosen such that the width of a ribbon conductor corresponds to the largest transverse extension of the opening.
EP-A2 0 165 632 describes an optical transmission element in which a stack of a plurality of ribbon conductors is mounted inside a tubular protective covering. In order to achieve a uniform loading of the optical fibers, this stack is inherently twisted, which requires a considerable outlay in terms of production and leads in any case to tensile, compressive and torsional stresses in the fibers. The excess length that can be produced in this way is extremely small, and the position of the ribbons in the cable itself becomes all the less defined the fewer ribbon conductors there are accommodated in the cable core.